The Language teaching "White Knight" Joseph has been helping folks so long here that he knows the tricks of "others" trades. (With the possible exception of spelling ammonia ).
I put this now in the docs:
for MULTICHOICE, which is shown with a dropdown, you cannot have any HTML formatting. If you need subscript or superscripts you can use ISO (Unicode)characters like this: {1:MULTICHOICE:H₂O~C₆H₁₂O₆~=NH₃} (see more about ISO sub/superscripts here: wikipedia)
Only after posting , I noticed I was in the 2.0 part of Docs. I think and hope this is equally true there. (And I haven't put it in 1.9)